Q: You mentioned having to identify flies in order to control them. What is the difference -- a fly is a fly, isn't it? So what? Are there different kinds that we should be concerned about?

A: There are a number of kinds of flies found in and around homes, and it is important to know the difference, as some can cause problems, some are an indicator of another problem and some are innocuous.

I monitor flies around my home with a simple fly trap. I cut the tops off several plastic water bottles and invert the tops into the lower portions, forming a funnel. I put about 2 inches of apple cider vinegar in each bottle with 1/4 teaspoon of sugar. Almost all flies, no matter their normal food preference, will enter the trap. I then pour them out through a sieve, let them dry and identify them.

The following flies are commonly found around homes:

-- House flies. These flies have a gray thorax (the part where the head is connected and wings are attached) with four dark stripes, and a mottled abdomen (posterior portion). These flies are considered "filth flies" and will feed on excrement, garbage, carcasses and even human secretions from wounds and mucous membranes. If you accidentally eat the larvae (maggots) in contaminated food, they can survive in your intestine.

-- Little houseflies. These common little flies resemble houseflies, but they fly in circles in the middle of a room or on a porch and don't appear to land. They can lay their eggs in any organic material, including compost piles, pet feces, dead leaves, etc. They have been known to enter the urinary tract of sleeping people and cause urinary myiasis.

-- Blowflies. These flies are larger than houseflies and are normally shiny green, blue, bronze or black. Blowflies feed on decaying animal matter, and if you have them in your house, it is an indication of a dead animal in the wall or ceiling. These flies are also used by forensic entomologists to establish the time of death in human fatalities.

-- Cluster flies. These flies resemble large houseflies but are more closely related to blowflies. They are not filth flies, as they parasitize earthworms. They do have the disconcerting habit of invading homes in large numbers in the fall to pass the winter. Sealing them out is the only practical way to deal with cluster flies.

-- Flesh flies. These flies resemble houseflies but differ in having only three stripes on a gray thorax. Some species lay their eggs in foul-smelling dead animal matter, while others lay their eggs in wounds on horses, cattle and other animals. There was a case several years ago where these flies laid their eggs in the festering wound of a person in a nursing home. One species can lay eggs in the noses or eyes of humans, causing myiasis, which can be serious.

Other flies also are common, but these are the most serious. You certainly don't want any of these flies around schools, day care centers, hospitals, nursing homes, animal shelters or other areas where they can infect people or animals. If you have a fly problem, electric fly traps work well, but they are expensive.

I use the apple cider vinegar trap at our place. Gallon-size milk jugs cut as described above and baited with apple cider vinegar and sugar will catch a lot of flies in a barn or other large building.

Of course if you don't recognize your flies, you can call a pest control professional. Any competent professional will instantly recognize all of the flies I mentioned. If they can't, I can ID them for you.

If you send bugs to be identified, here is how to mail them. Place them in a leak-proof vial of any type of alcohol, then pack the vial, very carefully padded, in a small box. (Otherwise, the vial often breaks and the post office will not deliver it.) Or you may pack bugs in cotton in a film canister or similar container. Bugs simply sent dry in an envelope are usually crushed beyond recognition.

Once the bugs are properly packaged, mail the package to Richard Fagerlund, P.O. Box 1173, Corrales, NM 87048. Be sure to include an e-mail address or a stamped, self-addressed envelope for the reply.

If you'd like, you may include a $10 check made out to me. A portion of the proceeds will be donated to animal rescue organizations.